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This study investigates the air quality impacts of using a high-blend ethanol fuel (E85) instead of gasoline in vehicles in an urban setting when a morning fog is present under summer and winter conditions. The model couples the near-explicit gas-phase Master Chemical Mechanism (MCM v. 3.1) with the extensive aqueous-phase Chemical Aqueous Phase Radical Mechanism (CAPRAM 3.0i) in SMVGEAR II, a fast and accurate ordinary differential equation solver. Summer and winter scenarios are investigated during a two day period in the South Coast Air Basin (SCAB) with all gasoline vehicles replaced by flex-fuel vehicles running on E85 in 2020. We find that E85 slightly increases ozone compared with gasoline in the presence or absence of a fog under summer conditions but increases ozone significantly relative to gasoline during winter conditions, although winter ozone is always lower than summer ozone. A new finding here is that a fog during summer may increase ozone after the fog disappears, due to chemistry alone. Temperatures were high enough in the summer to increase peroxy radical (RO 2 ) production with the morning fog, which led to the higher ozone after fog dissipation. A fog on a winter day decreases ozone after the fog. Within a fog, ozone is always lower than if no fog occurs. The sensitivity of the results to fog parameters like droplet size, liquid water content, fog duration and photolysis are investigated and discussed. The results support previous work suggesting that E85 and gasoline both enhance pollution with E85 enhancing pollution significantly more at low temperatures. Thus, neither E85 nor gasoline is a 'clean-burning' fuel.

[1] To date, gas photochemistry has not been simulated beyond a few hundred reactions in a three-dimensional (3-D) atmospheric model. Here, we treat 4675 gases and 13,626 tropospheric and stratospheric reactions in the 3-D GATOR-GCMOM climate-pollution model and compare results with data and with results from a condensed 152-gas/297-reaction mechanism when the model was nested at increasing resolution from the globe to California to Los Angeles. Gases included C 1 -C 12 organic degradation products and H-, O-, N-, Cl − , Br-, Fl-, and S-containing inorganics. Organic reactions were from the Master Chemical Mechanism. Photolysis coefficients for 2644 photoprocesses and heating rates for 1909 photolyzing gases were solved with an online radiative code in each grid cell using quantum yield/cross section data over 86 UV/visible wavelengths. Spatial/ temporal emissions of > 110 gases were derived from the 2005 U.S. National Emission Inventory. The condensed mechanism was a modified Carbon-Bond IV (MCBIV). Threeday simulation results indicate that the more-explicit mechanism reduced the O 3 gross error against data versus the MCBIV error against data by only ∼2 percentage points (from 28.3% to 26.5%) and NO 2 and HCHO by ∼6 percentage points in Los Angeles. While more-explicit photochemistry improved results, the condensed mechanism was not the main source of ozone error. The more explicit mechanism, which treated absorptive heating by more photolyzing gases, also resulted in a different magnitude of feedbacks to meteorological variables and back to gases themselves than did the less-explicit mechanism. The computer time for all processes in GATOR-GCMOM with the more explicit mechanism (solved with SMVGEAR II in all domains) was only ∼3.7 times that with the MCBIV despite the factors of 31 and 46 increases in numbers of species and reactions, respectively.Citation: Jacobson, M. Z., and D. L. Ginnebaugh (2010), Global-through-urban nested three-dimensional simulation of air pollution with a 13,600-reaction photochemical mechanism,

Car sharing is seen as an alternative to car ownership; however, for many households, this option may be unthinkable. In this study, we explore the idea of combining car sharing and vehicle ownership in order to change car purchase behavior to improve the environmental performance of the fleet. We consider the personal vehicle as a bundle of attributes. We look at the distinction between Bdaily use^and Binfrequent useâ ttributes. BInfrequent use^features are those that are only needed occasionally, e.g., a larger trunk, all-wheel drive, seating for 7, and long vehicle range. If the vehicle attributes could be unbundled, the personal vehicle would include only those features needed on a daily basis, with car sharing providing the Binfrequent use^features. We qualitatively explore what the carsharing service would need to look like to cover the Binfrequent use^needs and analyze if the existing services can provide these needs. We base our analysis on literature and interviews with experts and representatives from car sharing and rental car companies in California and Sweden. We find that car sharing today does not cover the needs for unbundling the vehicle. There are not enough Binfrequent use^vehicles available in these services. However, new business models and the growth of peer-to-peer car sharing are already begun to widen the vehicle models available.

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